1. Field of the Invention
The present invention relates to a technical field of temperature control for a heat processing apparatus, for example, a vertical-type heat processing apparatus, for carrying out a heat process, after placing a plurality of substrates, such as semiconductor wafers, on a substrate holding tool and carrying it into a reaction vessel.
2. Background Art
There is known a vertical-type heat processing apparatus to be used for providing a heat process, such as film forming due to CVD, oxidation, diffusion and the like, to semiconductor wafers (hereinafter, referred to as “wafers”) in a batch manner. This vertical-type heat processing apparatus includes a heating furnace and a vertical-type reaction vessel provided in the heating furnace. A bottom end opening of the reaction vessel is opened and closed by a cover. A wafer boat, which is the substrate holding tool, is mounted on the cover, and multiple wafers are held in the wafer boat in a shelf-like state. Thereafter, the wafer boat is carried in the reaction vessel by raising the cover, followed by performing a predetermined heating process.
FIG. 8 shows a conventional vertical-type heat processing apparatus, which includes a reaction vessel 102, having a double tube structure composed of an inner tube 100 and an outer tube 101, and a heater 103. A processing gas is supplied through the inner tube 100 from below, and is discharged through a space provided between the inner tube 100 and the outer tube 101, flowing downward. Reference numeral 104 designates a wafer boat, 105 is a cover, and W expresses a wafer or wafers. As a temperature control mode in such an apparatus, there are methods as shown in FIGS. 8(a) and 8(b). For convenience of illustration, the interior of the reaction vessel 102 is shown to be heated by a single heater 103. In fact, however, the heater 103 comprises, for example, five, divided components arranged in the vertical direction, each component being configured to provide zone control for each corresponding region. FIG. 8(a) shows an example in which temperature detecting sections 106 are provided, including, for example, five, thermocouples, corresponding to each heater 103, arranged between the inner tube 100 and the outer tube 101, thereby to perform the temperature control for the heaters 103 by using these temperature detecting sections 106. FIG. 8(b) shows an example in which temperature detecting sections 106 are provided to a supporting member 107 extending upward from the cover 105, the temperature detecting sections 106 comprising, for example, five, thermocouples, thereby to perform the temperature control for the heaters 103 by using these temperature detecting sections 106.
When the wafer boat 104 in which the wafers W are contained is carried in the reaction vessel 102 (upon the loading time), temperature change is likely to occur on an inner wall of the reaction vessel, or in this example, on an inner wall of the inner tube 100. Namely, the wafer boat 104, carried out from the interior of the reaction vessel 102 after a film forming process is ended, is cooled while processed wafers W are taken out from the boat and new wafers W are transferred into the boat. In addition, because relatively low temperature wafers W are loaded in the wafer boat 104, it is difficult to stabilize the temperature of the inner wall of the inner tube 100 upon the loading. For example, in the method shown in FIG. 8(a), since the temperature detecting sections 106 are located to be opposed to the heat processing atmosphere across the inner wall of the inner tube 100, the degree of lowering temperature on the temperature detecting sections 106 is smaller than the degree of lowering temperature on the inner wall of the inner tube 100. Thus, the power supply to each heater 103 tends to be insufficient, as such increasing the temperature drop of the inner wall.
In the method shown in FIG. 8(b), the temperature detecting sections 106 are not closely contacted with the inner wall of the inner tube 100, but are separated therefrom. In addition, each temperature detecting section 106 itself has a smaller heat capacity. Therefore, the value of temperature to be detected is lower than the actual temperature of the inner wall. While such a temperature drop can be addressed by controlling the detected lower temperature value to be returned to a desired value, the power supply to each heater 103 may tend to be unduly large, as such the temperature of the inner wall is likely to be excessively high. Alternatively, if employing such a configuration that the temperature detecting sections 106 are embedded in the inner wall of the inner tube 100, the temperature of the inner wall can be stabilized. However, this is not practical because the entire body of the inner tube 100 must be exchanged if any one of the temperature detecting sections 106 is disconnected.
If significant temperature change occurs in the inner wall of the inner tube 100, film peeling may tend to be caused by difference of coefficients of thermal expansion between the material of the reactions vessel, for example, quartz, and a thin film deposited on the inner wall, resulting in contamination due to particles or particle contamination. For example, a silicon nitride film is widely used in the so-called hard mask for use in etching, and possesses a higher dielectric constant, thus exhibiting electric properties equal to the silicon oxide film, even in the case of a physically greater film thickness. Therefore, the silicon nitride film is useful as a gate oxide film, a capping film for an interlayer isolation film, or the like. However, because of a significantly greater difference of coefficients of thermal expansion between the silicon nitride film and quartz, film peeling is likely to occur due to temperature change of the inner wall. Additionally, because of current tendency of designing a further miniaturized and thinner-filmed semiconductor device, the acceptable limit for particles has become quite critical. Therefore, phenomena that have not been considered significantly problematic tends to be conspicuous as factors of deteriorating the yield. Especially, the temperature change of the inner wall of the reaction vessel upon carrying in the wafer boat (or upon the loading time) is required to be suppressed to the utmost.
Patent Document 1 describes prediction of temperature of an object to be processed, based on detected values from a temperature sensor and a heating model, for preventing film peeling in the reaction vessel upon loading or unloading the wafer boat.
Patent Document 1: TOKUKAI No. 2005-159317, KOHO